The present invention relates to an air motor and, more particularly, to an axial air motor having a plurality of cylinders disposed around the axis of rotation of an output shaft in such a manner that the direction of movement of the pistons is parallel with the output shaft.
So-called axial motors have heretofore been well known in which a plurality of cylinders are disposed around the axis of rotation of an output shaft in such a manner as to extend parallel with said axis and pressure is applied to a swash plate mounted on the output shaft by means of pistons respectively received in the cylinders, thereby rotating the output shaft. Most of the axial motors are oil-hydraulic motors that use oil as a working fluid as shown in, for example, the specification of Japanese Patent Publication No. 54-38721, and air motors that use air as a working fluid have not heretofore been widely used.
More specifically, since air is used as a working fluid axial oil-hydraulic motors cannot be utilized as air motors without change or modification for the following reasons:
First, since air motors are generally rotated at higher speed than oil-hydraulic motors, the mass of movable parts of the former must be made smaller than the latter to as large an extent as possible so that inertia force is minimized.
Secondly, since air motors are rotated at higher speed than oil-hydraulic motors and the working pressure of the former is lower than that of the latter, the frictional resistance of working parts of the air motors must be minimized.
Thirdly, although in the case of oil-hydraulic motors the working fluid per se has a lubricating function, it is necessary in the case of air motors to contrive smooth lubrication between working parts in view of the fact that there has been a recent tendency to adopt the oilless method for air motors (wherein no lubricant is sprayed in air).